This invention relates to an image processing apparatus that reads the image on a document by raster scanning and which rotates it at the same time.
In image processing, the image on a document is read with an image scanner and subjected to various image processing operations including translation, rotation and deletion. Among those operations, rotation is performed to correct the image if it is read with document inclined. Consider, for example, the case where image information is to be read from a document with an image scanner. If the document set on the image processing apparatus is inclined, data is entered as the image remains inclined. Such image looks unseemly when it is displayed on the screen or printed to deliver a hard copy.
Conventionally, the tilting of input image has been corrected by methods that are applied to the image on an image memory that has been entered and stored in an inclined state. Examples of such methods include: rotating a binary image on the image memory through a predetermined angle and correcting the tilting image on the basis of the dispersive value of the white run length of each column of pixels in the rotated image (see Japanese Patent Unexamined Publication No. Hei. 2-56081); causing the image on an image memory to be displayed on the screen and the user designating a point on the screen to determine the inclination of the image, which is then corrected in position (see Japanese Patent Unexamined Publication No. Hei. 2-130595); and rotating a specified pixel in the image on the image memory by increments of a predetermined angle, determining the angle of image rotation in accordance with the area of each rectangular region defined by the specified pixel, and correcting the inclination of the image (see Japanese Patent Unexamined Publication No. Hei. 2-226372). However, these conventional methods involve various problems. The methods described in the specifications of Japanese Patent Unexamined Publication Nos. Hei. 2-56081 and Hei. 2-226372 require that the image be rotated several times in order to determine the angle of its inclination; as a result, much time is needed to detect the angle of image inclination. The method described in the specification of Japanese Patent Unexamined Publication No. Hei. 2-130595 involves cumbersome procedures for the user such as giving instructions for designating a point on the screen and determining the angle of image inclination. Furthermore, in each of those methods, the tilting image has to be stored (written into the image memory) before the correcting operation is started; since the image is both read from and written into the memory in the step of correction, there has been a limit on the efforts to shorten the processing time.
The aforementioned problems such as the cumbersome procedures and the prolonged processing time are not inherent in the correction of tilting image alone but they are generally associated with the case where the image on a document is read and subjected to rotation.